Method PUT is not allowed by Access-Control-Allow-Methods in preflight response

　　前端通过XHR请求后端服务时，出现了下图现象：

　　根据问题的描述可知，是遇到跨域问题了，为了支持跨域，需要在后端做一下处理，可以这样处理：

    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
        HttpServletRequest request = (HttpServletRequest) servletRequest;
        HttpServletResponse response = (HttpServletResponse) servletResponse;
        response.setHeader("Access-Control-Allow-Methods", "POST, GET, PATCH, DELETE, PUT, OPTIONS");
        filterChain.doFilter(servletRequest, servletResponse);
    }

　　具体的添加过程，可以参考此链接

　　https://www.cnblogs.com/bien94/p/13188699.html